Hydrodynamic Mechanism Of Semi-active Energy Harvester Through Flapping Foils

Abio-inspired flapping foil can be used to harvest kinetic energy from ocean current. This new concept of ocean current harvester has attracted wide attention, due to its environmentally friendly characteristics, as well as its high efficiency. To achieve such an energy harvesting system, mode coupling between multiple degrees of freedom is usually needed, which means controlling one motion mode while extracting energy via the other following mode. Our studies are carried out by computational fluid dynamic method. First, the maximum effective angle of attack and flapping frequency are examined. Through varying these two parameters, an optimal parametric space is identified, where the extracting energy reaches its maximum. Then, of more interests, the mass ratio between the wing and its surrounding fluid is investigated. The results show that the mass ratio significantly affects the energy extracting efficiency. During the parameters we have concerned in this paper, the efficiency increases along with the decrease of the mass ratio. This suggests that the mass ratio or inertial effects have to be taken into account when evaluating the performance of the flapping foil based energy harvesting system.